Apparatus for confirming stop of movable portion

ABSTRACT

A detection means 1 detects changes in impedance generated at a coil TC caused in response to indentations Py1 and Py2 and projections provided at the surface of a movable portion Rot to generate a detection signal thereof. A speed judgement circuit 2, to which the detection signal from the detection means is provided, continuously generates a high level output signal A2i when the detection signal e change interval becomes greater than a specific length of time. A level detection circuit 3, to which the detection signal e is provided, generates a high level output signal A1i when the detection signal e is at or above a specific level. An AND circuit 4, to which the output signal A2i from the speed judgement circuit 2 and the output signal A2i from the level detection circuit 3 are provided, generates an output signal Z resulting from AND calculation of the two output signals A1i and A2i. The delay in notification of movable portion stop is reduced and notification of movable portion stop is issued based upon verification that the coil TC is combined with the movable portion Rot in a normal manner and also verification that the movable portion Rot has been monitored until immediately before the stop of the movable portion Rot.

TECHNICAL FIELD

The present invention relates to an apparatus that confirms that amovable portion has stopped and, to be more specific, it relates to anapparatus that detects that the speed of a movable portion is at orbelow a specific value and outputs its detection signal as a movableportion stopped signal.

BACKGROUND ART

In an apparatus that includes a movable portion driven by a motor or thelike, i.e., a robot or the like, a safety device that allows theoperator to approach the apparatus only after it has been detected thatthe movable portion has completely stopped operation is required inorder to assure safety of the operator who must approach the apparatus.Such safety devices include the motor rotation stop detecting devicedisclosed in International Publication WO94/23303, which is capable ofreliably detecting that the rotation of the motor has stopped, includingrotation under inertia, and operates toward safety when the apparatushas had a failure, thereby providing a high degree of safety. However,the device disclosed in this prior art publication has two problems yetto be solved: i.e., one; a delay that is generated in issuingnotification of the stop because the device is not provided with afunction for detecting the rotation rate and two; since a bridge circuitis employed for the rotation sensor, adjustment of the bridge circuit isrequired.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an apparatus forconfirming stop of movable portion with which the delay in issuingnotification of the stop of the movable portion is reduced.

It is a further object of the present invention to provide an apparatusfor confirming stop of movable portion that is capable of issuingnotification of movable portion stop after detecting that a coil iscombined with the movable portion correctly, so that a danger state, inwhich the coil may come in contact with the movable portion, cannotoccur.

It is a further object of the present invention to provide an apparatusfor confirming stop of movable portion in which notification of movableportion stop is issued based upon verification that the movable portionhas been monitored until immediately before the issuance of suchnotification.

It is a still further object of the present invention to provide anapparatus for confirming stop of movable portion that is capable ofgenerating a signal at the time of startup to indicate stop of themovable portion based upon verification made via a startup switch.

It is a still further object of the present invention to provide anapparatus for confirming stop of movable portion that issuesnotification of movable portion stop based upon verification that themovable portion has been monitored, even at the time of startup.

It is a still further object of the present invention to provide anapparatus for confirming stop of movable portion that is capable ofreducing the delay time that elapses before the movable portion stoppedsignal ceases when the movable portion has started to rotate or move.

It is a still further object of the present invention to provide anapparatus for confirming stop of movable portion that facilitatesadjustment.

In order to achieve the objects described above, the apparatus forconfirming stop of movable portion according to the present inventioncomprises a detection means, a speed judgement circuit, a leveldetection circuit and an AND circuit.

The detection means includes a coil that is provided in close proximityto a surface of the movable portion to detect changes in impedance atthe coil caused by indentations and projections provided at the surfaceof the movable portion and to generate a detection signal therefrom. Thedetection signal output from the detection means is provided to thespeed judgement circuit and when the detection signal change intervalbecomes greater than specific length of time, the speed judgementcircuit generates a sustained high level output signal. The detectionsignal output from the detection means is also provided to a leveldetection circuit and when the detection signal is at or above aspecific level, the level detection circuit generates a high leveloutput signal. The output signals from the speed judgement circuit andthe level detection circuit are provided to the AND circuit and the ANDcircuit generates an output signal that is resulting from the ANDcalculation of the two output signals.

As described above, in the apparatus for confirming stop of movableportion according to the present invention, the detection means includesa coil provided in close proximity to a surface of the movable portionto detect changes in impedance at the coil caused by indentations andprojections provided at the surface of the movable portion. When themovable portion is constituted of a rotating body, the time intervalsover which the coil encounters the indentations and projections providedat the surface of the movable portion change in correspondence to therotation rate so that the slower the rotation rate, the longer the timeintervals. Similarly, if the movable portion travels in a lineardirection, the time intervals change in correspondence to the movingspeed of the movable portion so that the slower is the moving speed, thelonger the time intervals. Since the impedance at the coil changes incorrespondence to changes in the time intervals which, in turn, concurwith changes in the rotation rate or the moving speed of the movableportion, the time intervals over which the detection signal changesbecome longer as the rotation rate or the moving speed of the movableportion become lower. The operating modes of the movable portion mayinclude both rotary and linear movement. Hereafter, for the purpose ofsimplifying the explanation, it is assumed that the movable portionperforms rotation that includes linear motion.

The speed judgement circuit, to which the detection signal output fromthe detection means is provided, generates a high level output signalcontinuously when the detection signal change interval becomes equal toor greater than a specific length of time. As explained earlier, sincethe time intervals with which the detection signal changes become longeras the rotation rate of the movable portion becomes lower, it is assumedthat the movable portion has stopped when the detection signal changeinterval becomes greater than the specific length of time and a highlevel output signal, which indicates stop of the movable portion, isgenerated. With this, the delay in notifying that the movable portionhas stopped can be reduced. The high level output signal indicating thatthe movable portion has stopped is output continuously to preventchattering of the notification of movable portion stop.

The level detection circuit to which the detection signal output fromthe detection means is provided, generates a high level output signalwhen the detection signal is at or above a specific level. The leveldetection circuit monitors the distance between the coil included in thedetection means and the movable portion, and outputs a low level outputsignal as a danger signal when the distance becomes reduced and a dangerstate arises, in which the movable portion and the coil may come incontact with each other.

Since the AND circuit, to which the output signals from both the speedjudgement circuit and the level detection circuit are provided,generates an output signal comprising the AND calculation of the twooutput signals, notification of movable portion stop can be issued afterdetecting that the coil and the movable portion are combined correctlywithout a danger state arising in which the coil may come in contactwith the movable portion.

In addition, the apparatus for confirming stop of movable portionaccording to the present invention may include a self holding circuit.The self holding circuit uses changes in the output signal from thedetection means as a trigger input signal and uses the output signalfrom the speed judgement circuit as a reset input signal. The ANDcircuit, to which the output signals from the self holding circuit andthe level detection circuit are provided, generates an output signalcomprising the AND calculation of the two output signals. When themovable portion is rotating, the output signal from the detection meanschanges in conformance to the changes caused by the indentations andprojections provided at the surface of the movable portion as explainedearlier. Since the self holding circuit uses changes in the outputsignal from the detection means as a trigger input signal, it, ineffect, constantly monitors the rotation of the movable portion. Theself holding circuit, to which a reset input signal constituted of anoutput signal from the speed judgement circuit is provided uponreceiving the provided trigger input signal mentioned above, generates ahigh level holding output when the reset input signal is set to high.Consequently, with the present invention, the notification of movableportion stop is issued based upon verification that the movable portionhas been monitored until immediately before the notification.

The AND circuit, to which the output signals from the self holdingcircuit and the level detection circuit are provided, generates anoutput signal resulting from the AND calculation of the two outputsignals. As a result, notification of movable portion stop can be issuedbased upon verification that the coil and the movable portion arecombined correctly so that a danger state, in which they may come incontact with each other, does not arise and also based upon verificationthat the movable portion has been monitored until immediately before theissuance of the notification of movable portion stop.

When the self holding circuit described above is provided, a means forstartup switching that is operated from the outside may also beprovided. The means for startup switching is, in turn, provided with acontact point for providing the self holding circuit with the triggerinput signal. Without such a means for startup switching provided, ifthe movable portion is not rotating at the time of startup, a triggerinput signal cannot be sent to the self holding circuit and,consequently, even when the reset input signal provided by the speedjudgement circuit is set to high, the output signal from the selfholding circuit is not set to high. The means for startup switching isprovided to eliminate this problem arising at the time of startup. Thismeans for startup switching has a contact point for providing the selfholding circuit with a trigger input signal so that a signal indicatingmovable portion stop can be generated based upon verification made bythe means for startup switching.

Preferably, the means for startup switching should be provided withanother contact point which is closed when the trigger input signal isturned off. In this case, the present invention should further includeanother AND circuit. This other AND circuit generates an AND outputusing the signal provided through the other contact point mentionedabove of the means for startup switching when the trigger input signalfor the self holding circuit is turned off and the output signal fromthe self holding circuit as its input signals. If the means for startupswitching is provided only with the contact point for providing atrigger input signal and an error occurs whereby a sustained triggersignal is provided to the self holding circuit through this contactpoint, such an error will result in a further error, in which the selfholding circuit outputs a sustained high level signal. In contrast, byproviding another contact point which is closed when the trigger inputsignal is turned off in the means for startup switching and alsoproviding the other AND circuit described above, the error mentionedabove can be avoided, and even at the time of startup, the notificationof movable portion stop can be issued based upon verification of movableportion monitoring.

Furthermore, in the apparatus for confirming stop of movable portionaccording to the present invention, the speed judgement circuit mayinclude two on-delay circuits and an off-delay circuit. The two on-delaycircuits, to which the signal output from the detection means, whichincludes the detection signal, is commonly provided, generate outputsignals whose phases are the inverse of each other. The off-delaycircuit is provided with an OR signal comprised of the output signalsfrom the two on-delay circuits. In this structure, the signal indicatingmovable portion stop can be turned off promptly when the movable portionhas started rotating or traveling.

Moreover, in the apparatus for confirming stop of movable portionaccording to the present invention, the coil may constitute a resonancecircuit which includes the movable portion. Since the movable portion isprovided with indentations and projections on its surface, the resonancefrequency of the resonance circuit constituted with the coil and themovable portion changes depending upon whether the coil is detecting anindentation or a projection. When the resonance frequency to be detectedis specifically set at the frequency when the coil is detecting anindentation, the level of the detection signal obtained by the resonancecharacteristics of a projection is lower than the level of the detectionsignal obtained in conformance to the resonance characteristics of anindentation. In addition, when the coil has dropped, the resonancecharacteristics will be different from the resonance characteristicsobtained from either the indentations or the projections. Thus, basedupon the differences in the resonance characteristics, errors such asthe coil dropping and the like, as well as the rotation or travel of themovable portion can be detected without employing a bridge circuit. As aresult, an apparatus for confirming stop of movable portion thatfacilitates adjustment can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the invention and the concomitantadvantages will be better understood and appreciated by persons skilledin the field to which the invention pertains in view of the followingdescription given in conjunction with the accompanying drawings whichillustrate preferred embodiments. In the drawings:

FIG. 1 is a block diagram of the apparatus for confirming stop ofmovable portion according to the present invention;

FIG. 2 shows a specific example of the apparatus for confirming stop ofmovable portion according to the present invention shown in FIG. 1;

FIG. 3 shows the relationship between the coil and the movable portionin the apparatus for confirming stop of movable portion according to thepresent invention shown in FIGS. 1 and 2 ;

FIG . 4 shows the frequency-detection signal characteristics withvarious combinations of the coil and the movable portion shown in FIG.3;

FIG. 5 shows a time chart illustrating the operation of the apparatusfor confirming stop of movable portion shown in FIG. 2;

FIG. 6 is a block diagram of another embodiment of the apparatus forconfirming stop of movable portion according to the present invention;

FIG. 7 shows a specific example of the apparatus for confirming stop ofmovable portion according to the present invention shown in FIG. 6;

FIG. 8 is another specific example of the apparatus for confirming stopof movable portion according to the present invention shown in FIG. 6;

FIG. 9 shows improved frequency-detection signal characteristics withthe combination of the coil and the movable portion shown in FIG. 2;

FIG. 10 is an electric circuit diagram illustrating yet another exampleof the speed judgement circuit included in the apparatus for confirmingstop of movable portion according to the present invention;

FIG. 11 shows a time chart of the operation performed when the speedjudgement circuit shown in FIG. 10 is employed, and;

FIG. 12 is an electric circuit diagram of an example of a variation ofthe speed judgement circuit shown in FIG. 10.

BEST MODE FOR CARRYING OUT THE INVENTION

The apparatus for confirming stop of movable portion according to thepresent invention shown in FIG. 1 includes a detection means 1, a speedjudgement circuit 2, a level detection circuit 3 and an AND circuit 4.Rot indicates a metal movable portion that rotates in the directionindicated with the arrow Cn with an output from a motor or the like, andPy1 and Py2 indicate indentations or holes provided in the movableportion Rot. In the movable portion Rot in the figure, the areas of thesurface where the indentations or holes Py1 and Py2 are not providedconstitute projections.

The detection means 1 includes a coil TC, which is provided in closeproximity to a surface of the movable portion Rot over a distance L. Thedetection means 1 detects changes in impedance generated at the coil TCcaused in response to the indentations or holes Py1 and Py2 (hereafterreferred to as the indentations Py1 and Py2) provided at the surface ofthe movable portion Rot, and outputs a detection signal thereof. Thedetection means 1 includes a sensor circuit Rse, which detects thechanges in impedance at the coil TC, which is separated from the movableportion Rot by the distance L, that are generated in correspondence tothe presence or absence of the indentations Py1 and Py2.

The speed judgement circuit 2, to which the detection signal e outputfrom the detection means 1 is provided, outputs a high level outputsignal A2i (logical value 1), when the signal e indicates a specificspeed or lower. The signal that indicates rotation is generatedaccording to changes in the output signal e of the sensor circuit Rseresulting from changes in impedance at the coil TC caused by theindentations Py1 and Py2 at the surface of the metal movable portionRot.

The level detection circuit 3, to which the detection signal e is alsooutput from the detection means 1, generates an output signal A1i athigh level (logical value 1) when the detection signal e is at or higherthan a specific level. The level detection circuit 3 is provided tomonitor the distance L between the coil TC and the movable portion Rot.

The AND circuit 4, to which the output signals A1i and A2i are providedfrom the level detection circuit 3 and the speed judgement circuit 2respectively, generates an output signal Z resulting from the ANDcalculation of the two output signals A1i and A2i. While the coil TCmaintains a normal distance L relative to the surface of the movableportion Rot, if the output signal A1i of the level detection circuit 3is at high level (logical value 1) and the output signal A2i of thespeed judgement circuit 2 has logical value 1, the output signal Z ofthe AND circuit 4 is at high level (logical value 1) to indicate thatthe movable portion is stopped. If the logical value of either of theinput signals is 0, the output signal Z is set to low level (logicalvalue 0).

As explained above, in the apparatus for confirming stop of movableportion according to the present invention, the detection means 1includes the coil TC provided in close proximity to the surface of themovable portion Rot so that the detection means 1 can detect changes inimpedance generated at the coil TC caused in response to indentationsPy1 and Py2 provided at the surface of the movable portion Rot. The timeintervals with which the coil TC responds to the indentations Py1 andPy2 provided at the surface of the movable portion Rot change incorrespondence to the rotation rate if the movable portion Rot is arotating body, and the lower the rotation rate, the longer the timeintervals. In addition, when the movable portion Rot moves linearly, thetime intervals change in correspondence to the moving speed, and thelower the moving speed, the longer the time intervals. Since the changesof impedance at the coil TC correspond to time intervals that change asthe rotation rate or moving speed of the movable portion Rot changes,the change time interval in the detection signal e becomes longer as therotation rate or moving speed of the movable portion Rot becomes lower.

The speed judgement circuit 2, to which the detection signal e outputfrom the detection means 1 is provided, continuously generates theoutput signal A2i at high level (logical value 1) when the change timeinterval of the detection signal e is at a specific length of time orlonger. Since the change time interval of the detection signal e becomeslonger as the rotation rate or moving speed of the movable portion Rotbecomes lower, the movable portion is assumed to have stopped when thedetection signal e change time interval becomes equal to or longer thana specific length of time, and the output signal A2i at high level(logical value 1) is generated, which indicates that the movable portionhas stopped. With this, the delay in issuing notification of stop of themovable portion Rot is reduced. The output signal A2i at high level(logical value 1) indicating movable portion stop is outputcontinuously. Thus, chattering of the movable portion stop notificationis prevented.

The level detection circuit 3, to which the detection signal e outputfrom the detection means 1 is provided, generates the output signal A1iat high level (logical value 1) when the detection signal e is at orover a specific level. Thus, when a state arises in which the distance Lis reduced and the coil TC might come in contact with the movableportion Rot, an output signal A1i at low level (logical value 0) isoutput as a danger signal.

The AND circuit 4, to which the output signals A1i and A2i are providedfrom the level detection circuit 3 and the speed judgement circuit 2respectively, generates the output signal Z resulting from the ANDcalculation of the two output with signals A1i and A2i. Consequently, itis possible to issue notification of movable portion stop upon detectingthat there is no danger state arising in which the coil TC may come incontact with the movable portion Rot.

International Publication WO 94/2303 discloses features such as: asignal for indicating rotation included in the output signal of thesensor circuit; the level detection circuit monitors to ensure that theoutput signal is within a specific level range; a rotation stopdetection circuit that generates a high level output signal (logicalvalue 1) when the rotation signal included in the output signal goes off(indicating stop of rotation) and the AND calculation output signal ofthe output signal from the level detection circuit and the output signalfrom the rotation stop detection circuit is used as an output signalindicating rotation stop. However, this prior art technology does notinclude a movable portion speed judgement circuit. Thus, in order toachieve the movable portion speed judgment, a special contrivance isrequired. A specific example of this is explained below.

FIG. 2 shows a specific example of circuit configuration of theapparatus for confirming stop of movable portion shown in FIG. 1. InFIG. 2, the detection means 1 includes the coil TC and the sensorcircuit Rse. An AC signal output from a signal generator SG1 is providedto a first winding N1 of the coil TC via a current limiting resistanceR1. The AC signal induced to a second winding N2 is amplified at anamplifier A1 and the output signal from the amplifier A1 is rectifiedand smoothed by a rectifying circuit RC1 so that it becomes a DC outputsignal e. The coil TC is provided with a resonance capacitor Cr whichresonates at the operating frequency of the AC signal provided by thesignal generator SG1.

The changes in impedance of the coil TC caused in response to theindentations Py1 and Py2 at the surface of the movable portion Rot (seeFIG. 1) manifests as changes in the output signal e from the rectifyingcircuit RC1. Note that the structure of the coil TC is not necessarilylimited to the structure shown in the figure. For instance, it may beprovided with only one winding. Apart from that, a variety of coilstructures to constitute an electromagnetic induction sensor may beadopted.

FIG. 3 is an enlarged view of a structure in which the movable portionRot constituted with, for instance, an iron plate, is provided at thefront of the coil TC. FIG. 4 shows changes in the rectified outputsignal e when the coil TC and the movable portion Rot are positioned asshown in FIG. 3. When the movable portion Rot is not present, therectified output signal e is equivalent to a curve with L=∞. Thisapproximately corresponds to a case in which the indentations Py1 andPy2 in FIGS. 1 and 2 constitute large holes with bottoms and the coil TCfaces opposite the indentations Py1 and Py2. When the excitationfrequency f of the coil TC is at the resonance frequency fr, the outputvoltage e=e0 with L=∞. When the coil TC faces opposite a surfaceconstituting a projection of the movable portion Rot, the output signale is reduced to e=e1 with the distance L=L1, and is reduced to e=e2(e1>e2) with L=L2 (L2<L1). Consequently, when the distance L between themovable portion Rot and the coil TC is set at the distance L1, theoutput signal e changes between the output voltage e0 and the outputvoltage e1 as the movable portion rotates.

In FIG. 4, the level of the voltage et constitutes the threshold valueof the level detection circuit 3 (FIG. 2) and when the rectified outputsignal e is at or lower than the threshold value et, the output signalA1i of the level detection circuit 3 becomes a low level output signalwith a logical value of 0 whereas, when the rectified output signal e isat a level higher than the threshold value et, the output signal A1i ofthe level detection circuit 3 is a high level output signal with alogical value of 1. Thus, if the coil TC approaches the surface of themovable portion Rot so that the distance L=L2, the output signal of thelevel detection circuit 3 will have a logical value of 0. Consequently,if a state in which the distance L is reduced and the coil TC may comeinto contact with the movable portion Rot, the output signal A1i at lowlevel (logical value 0) is output as a danger signal to avoid the dangerof the coil TC coming into contact with the movable portion Rot.

Next, the structure and operation of the speed judgement circuit 2 areexplained. The speed judgement circuit 2 which is enclosed with thechain lines in FIG. 2, includes an amplifier A2 which amplifies thechange in the output signal e output of the rectifying circuit RC1 ofthe detection means 1, a rectifying circuit RC2 for generating theenvelope detection output of the output signal from the amplifier A2, alevel detection circuit LV1, an on-delay circuit OND for determining therotation rate and an off-delay circuit OFD for generating an outputsignal at a high output level with a logical value of 1 after themovable portion Rot enters a low speed rotation state prior to stoppinguntil the movable portion Rot enters a high speed rotation state again.The output signal from the off-delay circuit OFD becomes an input signalof the AND circuit 4 as the output signal A2i of the speed judgementcircuit 2 along with the output signal A1i of the level detectioncircuit 3.

When constituting the level detection circuit 3, the LV1 and the ANDcircuit 4 as fail-safe elements, one of the fail-safe windowcomparator/AND gates disclosed in U.S. Pat. No. 5, 345,138, U.S. Pat.No. 4,661,880 and U.S. Pat. No. 5,027,114 may be used. The same appliesto the level detection circuits LV1, LV2 and the AND circuit 4, whichare to be explained later.

The changes in the output signal e from the rectifying circuit RC1 areinput to an amplifier A2 via a coupling capacitor C1. In this case, if adisconnection failure should occur in the capacitor C1, the rotationsignal generated at the rectifying circuit RC1 (changes in the rectifiedoutput signal e) is not communicated to the amplifier A2 and, as aresult, the speed judgement circuit 2 may indicate a rotation stop stateeven when the movable portion is rotating. In order to ensure that sucha problem does not occur, a signal generator SG2 is provided in thisembodiment. A high frequency output signal w from the signal generatorSG2, set at low level (logical value 0), is superimposed on the outputsignal from the rectifying circuit RC1 via a resistance R3. The outputfrequency of the signal generator SG2 is high enough to ensure that thecapacitance of the smoothing capacitor included in the rectifyingcircuit RC1 does not work as a load impedance. Because of this, theoutput signal w of the signal generator SG2 is input to the amplifier A2at a signal level achieved by dividing the voltage between theresistance R3 and a resistance R2. The technology through which arotation signal is monitored while taking into consideration a possibledisconnection failure of the coupling capacitor C1 is disclosed in theInternational Publication WO 94/23303 described earlier.

In addition, if the change in the output signal of the rectifyingcircuit RC1, which occurs as the movable portion Rot rotates, contain aDC component, a clamp amplifying circuit constituted with a diode may beemployed for an AC amplifying circuit which is constituted with thecoupling capacitor C1 and the amplifier A1. A state in which the changein the output signal of the rectifying circuit RC1, which occurs as themovable portion Rot rotates, contains a DC component may occur when thetime width over which the output signal is at high level (logicalvalue 1) with e=e0, differs from the time width over which the outputsignal is at low level (logical value 0) with e=e1, for instance. Thetechnology that employs a clamp amplifying circuit for an input signalwith different lengths of sustaining time over which it remains at highlevel (logical value 1) and over which it remains at low level (logicalvalue 0), is already known through the disclosures made in JapaneseExamined Patent Publication Nos. 4320/1980 and 34396/1975.

Next, the principle structure and the operation of the speed judgementcircuit 2 shown in FIG. 2 are explained in reference to the time chartshown in FIG. 5.

In FIG. 5, a time block t1 on a time axis t constitutes a time periodduring which the movable portion Rot is in a stopped state prior tostarting to rotate. Time block t2 constitutes a time period over whichthe movable portion Rot is in a transition state during which themovable portion Rot shifts from a rotating state to a stopped state andtime block t3 is a time period over which the movable portion Rot isassumed to have reached the stopped state. Time Chart (a) shows theoutput signal e of the rectifying circuit RC1. During the time block t1,over which the movable portion Rot is in a stopped state, the outputsignal e indicates a specific value at a level which is between themaximum value e0 and the minimum value e1 of the changes in amplitudewhich occur as the movable portion Rot rotates. During the time blockt2, the cycle of the changes in amplitude of the output signal eincreases as the rotation of the movable portion Rot slows down. In thetime block t3, during which the movable portion Rot has entered astopped state, the stop is shown as occurring at a position between theindentations Py1 and Py2 in the movable portion Rot shown in FIG. 1, forinstance.

Time Chart (b) shows a state in which the output signal w that is outputfrom the signal generator SG2 is superimposed on the signal e.

Time Chart (c) shows an output signal resulting from the signal w beinginput to the amplifier A2 via the capacitor C1 to be amplified. In thevicinity of the apex of the change in the signal e, since the inputlevel is high, the amplifier A2 becomes saturated and the components ofthe signal w disappear. The components of the amplified signal w aregenerated only in the vicinity of the zero point, which corresponds tothe vicinity of the level that represents the average value of thesignal e.

At the rectifying circuit RC2 on the output side of the amplifier A2,since the capacitance of the coupling capacitor C2 is sufficientlylarge, the change in the signal e, which results from the rotation, ismanifested directly as a terminal voltage at a smoothing capacitor C3.The capacitance of the smoothing capacitor C3 is set to ensure that onlythe high frequency signal w is smoothed. Because of this, as shown inTime Chart (d), only the high frequency signal w of the terminal voltageof the smoothing capacitor C3 is rectified and smoothed, and the portionrepresenting the change in the signal e in the output signal of theamplifying circuit A2 is directly output between the terminals of thecapacitor C3.

The output signal of the level detection circuit LV1, too, follows apattern similar to that shown in Time Chart (d). In other words, therectifying circuit RC2 and the level detection circuit LV1 constitute alow pass filter through which a high level (logical value 1) outputsignal is generated relative to a high frequency input signal and anoutput signal responds to a low frequency input signal.

Since the movable portion Rot is in a stopped state during the timeblock t1, only the high frequency signal w is amplified at the amplifierA2, which is then output as an output signal k2 at high level (logicalvalue 1) of the rectifying circuit RC2.

While the time block t3 represents a state in which the movable portionRot has stopped after completion of the change P1 in the signal e, themovable portion Rot may, in fact, have moved slightly after passing overthe indentations Py1 and Py2 before reaching the next indentation Py1 orPy2. The amplifier A2 amplifies this change and no component of thesignal w is generated at the coupling capacitor C1 until the electriccharge accumulated because of the change has been discharged. The riseof the signal during the time block t4 in Time chart (c) and (d)represent this fact. The level Th2 entered in Time Chart (d) indicatesthe threshold value of the level detection circuit LV1.

The on-delay circuit OND measures the length of time over which a highlevel state is sustained in the level detection circuit LV1. In a DChigh level state, the state of maximum level output is indicated withlogical value 1 while the low level state corresponds to logical value0. The on-delay circuit OND generates a high level (logical value 1)output signal k5 (see Time Chart (g)) when a specific delay time Ton haselapsed after a high level (logical value 1) input signal k4 is input.This signal k5 with a logical value of 1 signifies that the movement ofthe movable portion Rot is at or has fallen under a specific speed.Then, if the input signal k4 (see Time Chart (f)) does not remain in ahigh level state (logical value 1) until the delay time Ton has elapsedand the logical value 0 is set within a short time t<Ton, the on-delaycircuit OND measures again the period of time over which the high levelstate is sustained the next time a high level (logical value 1) inputsignal is generated, and generates a high level (logical value 1) outputsignal k5 after the specific length of time Ton has elapsed. Circuit sprovided with such a function already exist in the known art, asdisclosed in the International Publication WO 94/723303 mentionedearlier and in Japanese Examined Patent Publication No. 23006/71989.

Since the output signal k5 with the logical value of 1 that is outputfrom then on-delay circuit OND i s generated only when the input signalk4 is at high level (logical value 1), as shown in Time Chart (g), theoutput signal with the logical value of 1 is generated only when thesignal k4 is at high level (logical value 1) even after the movableportion Rot is rotating at a speed at or lower than a specific leveland, therefore, it is intermittent. The off-delay circuit OFD isprovided with a function for holding the output signal k5 of theon-delay circuit OND which is generated intermittently as explainedabove. As shown in FIG. 1, in a structure in which the rotation of themovable portion Rot is detected intermittently with the timing withwhich the coil TC comes face to face with the indentations Py1 and Py2,it is necessary to hold the signal indicating detection of theindication Py1 during the period of time after the signal generated bythe detection of, for instance, the indentation Py1 by the coil TC isreceived until the signal indicating detection of the indentation Py2 issubsequently received. The off-delay circuit OFD is provided to assuresuch a holding function. In the embodiment shown in FIG. 2, the signalk5, which is output at a high level (logical value 1) from the on-delaycircuit OND is integrated by a diode D3 and a capacitor C4 and its levelis detected by the level detection circuit LV2. The discharge of theelectrical charge which has accumulated in the capacitor C4 is performedthrough the input resistance of the level detection circuit LV2. Withthis, the intermittent output signal k5 of the on-delay circuit OND isconverted to a sustained high level (logical value 1) output signal k6(see Time Chart (h)).

In FIG. 2, the output signal of the rectifying circuit is shown in acircuit configuration in which it is clamped at the source potentialVcc. The reason for this is that the output signals of the amplifiers A1and A2 and the signals processed at the level detection circuits and theon-delay circuit are AC signals and that input signals at a level higherthan that of the source potential are required for the input signals forthe level detection circuits and the on-delay circuit.

Next, in reference to FIGS. 6 to 12, another embodiment of the apparatusfor confirming stop of movable portion according to the presentinvention is explained. In these figures, the same reference numbers asthose in FIGS. 1 to 5 are assigned to identical components.

First, in FIG. 6, tthe apparatus for confirming stop of movable portionincludes a self holding circuit 5. The self holding circuit 5 uses thechange in the output signal of the detection means 1 as a trigger inputsignal and uses the output signal k6 of the speed judgement circuit 2 asa reset input signal. The AND circuit 4, to which the output signals A2iand A1i are provided from the self holding circuit 5 and the leveldetection circuit 3 respectively, generates an output signal Z resultingfrom the AND calculation of the two output signals A2i and A1i. When themovable portion Rot is rotating or moving, the output signal e of thedetection means 1 changes in conformance to the indentations andprojections provided at the surface of the movable portion Rot, asexplained earlier.

The operation of the embodiment shown in FIG. 6 may be explained inreference to the time chart shown in FIG. 5. Since the self holdingcircuit 5 uses change in the output signal e of the detection means 1 asa trigger input signal, the rotation or movement of the movable portionRot is monitored at all times. The self holding circuit 5, uponreceiving the trigger input signal described above, is further providedwith a reset input signal k6 (see Time Chart (h) in FIG. 5) which isconstituted from the output signal of the speed judgement circuit 2, andwhen the reset input signal is set to high (logical value 1), the selfholding circuit 5 generates a high level (logical value 1) holdingoutput k8 (see Time Chart (i) in FIG. 5). As a result, in thisembodiment, the notification of movable portion stop is issued basedupon verification that the movable portion Rot has been monitored untilimmediately before the notification is issued.

The AND circuit 4, to which the output signals A2i and A1i are providedfrom the self holding circuit 5 and the level detection circuit 3respectively, generates the output signal Z resulting from the ANDcalculation of the two output signals A2i and A1i. Consequently,notification that the movable portion has stopped can be issued basedupon verification that the movable portion Rot has been monitored untilimmediately before the notification of movable portion stop is issuedand based upon verification that the detection means 1 is combined withthe movable portion Rot correctly without causing an error such asfalling down.

In the embodiment shown in the figure, a means for rotation detection 6is provided. The means for rotation detection 6 is a circuit fordetecting rotation. With this means for rotation detection 6, a signalindicating rotation is extracted from the speed judgement circuit 2 andits output signal k7 is used as a trigger input signal for the selfholding circuit 5 and the output signal k6 of the speed judgementcircuit 2 is used as a reset signal while output signal k8 of the selfholding circuit 5 is used as an input signal at the AND circuit 4.

FIG. 7 shows a more detailed circuit configuration of the apparatus forconfirming stop of movable portion shown in FIG. 6. In the figure,reference numbers that are the same as those in FIG. 2 indicateidentical components. In FIG. 7, an output signal k1 of the amplifierA2, which constitutes a component of the speed judgement circuit 2 isinput to the means for rotation detection 6, and an output signal k7 ofthis means for rotation detection 6 becomes a trigger input signal forthe self holding circuit 5. The means for rotation detection 6 includesa current limiting resistance R4, a 4-terminal capacitor C5, a couplingcapacitor C6 and a discharge resistance R5. While the capacitor C6 andthe resistance R5 constitute a differentiating circuit, if this timeconstant is large, the change in the voltage between the terminals ofthe capacitor C5 is directly used as a trigger input signal of the selfholding circuit 5.

The signal k1, which is shown in Time Chart (c) in FIG. 5 is input tothe capacitor C5 via the resistance R4. The resistance R4 is inserted sothat the capacitor C5 does not affect the output side of the amplifierA2. As in the case of the capacitor C3, the capacitance of the capacitorC5 has a low impedance relative to the high frequency signal w and,consequently, a terminal voltage signal k3 of the capacitor C5 is asignal similar to that shown in Time Chart (d). The rise of the signalk3 becomes a trigger signal of the self holding circuit 5 via thecapacitor C6.

The self holding circuit 5 uses the output signal k6 of the off-delaycircuit OFD of the speed judgement circuit 2 as a reset signal. Afterthe output signal k6 of the off-delay circuit OFD rises, its outputsignal k8 is generated at time point t5 concurrently with the rise ofthe output signal k6 when the capacitance of the coupling capacitor C6is large, and is generated at the point in time (time point t6) at whichthe terminal voltage of the capacitor C5 has risen next time when thecapacitance of the coupling capacitor C6 is small, since the triggerinput signal becomes a differential signal in that case, as shown inTime Chart (i) in FIG. 5.

In such a structure, even if the coil TC drops during rotation of themovable portion Rot, no output signal that erroneously indicates stop ofrotation will be generated. In other words, in the apparatus forconfirming stop of movable portion shown in FIG. 7, the movable portionRot is monitored until immediately before the stop signal k8 with alogical value of 1 is generated. The self holding circuit may beconstituted by employing a circuit in the known art such as thosedisclosed in International Publication WO 94/23303 and InternationalPublication WO 94/23496.

FIG. 8 shows yet another embodiment of the apparatus for confirming stopof movable portion according to the present invention.

In the embodiment shown in FIGS. 6 and 7, unless the movable portion Rotis not rotating when the source voltage Vcc is applied, the outputsignal of the self holding circuit 5 does not enter a high level statewith a logical value of 1, which indicates stop of rotation. Theembodiment shown in FIG. 8 provides a solution to this problem. As ameans for achieving the solution, the device in FIG. 8 is provided witha switch 7. If the movable portion Rot is stopped at startup, thelogical value of the output signal k6 of the off-delay circuit OFD isset to 1. In this state, the switch 7 is connected to the side of acontact point Bon to set it to on in order to forcibly provide the selfholding circuit 5 with a DC input signal Va at high level (logicalvalue 1) as a trigger input signal. With this, the output signal k8 ofthe self holding circuit 5 enters a high level state with the logicalvalue 1, which indicates stop of rotation and, as a result, even atstartup, the output signal k8 of the self holding circuit 5 can be setin a high level state which corresponds to the stop of rotation of themovable portion.

If an error occurs such as the contact point on the Bon side remainingin a closed state, the input signal Va supplied from the outside will beconstantly input and the self holding circuit 5 will, at all times,generate an output whose logical value is 1. As a means for avoidingsuch a condition, an AND circuit 8 is provided. By reversing the switch7 from the contact point Bon to a contact point Bof, a high level inputsignal Va is provided to the AND circuit 8 through the contact point Bofand the AND circuit 8 uses the AND output signal of this input signal Vaand the output signal k8 of the self holding circuit 5 as an inputsignal A2i for the AND circuit 4. As a result, since the output signalk8 output of the self holding circuit 5 is set to high only when anormal trigger input signal resulting from stop of rotation of themovable portion Rot is provided by the rotation detection circuit 6, theerror described above does not occur.

Next, in reference to FIG. 9, yet another embodiment is explained. Inthe embodiment shown in FIGS. 6 and 7, if the coil TC has alreadydropped at startup, an erroneous stop verification signal Z will begenerated. Taking into consideration the possible falling down of thecoil, the device disclosed in the International Publication WO 94/2303mentioned earlier is provided with a coil on one side of the bridgecircuit to ensure that an output signal for stop verification isgenerated only within a limited range of distance between the metalmovable portion and the coil. As a means for achieving this, the leveldetection circuit is constituted with a so-called window comparatorcircuit, having upper limit and lower limit threshold values. However, abridge circuit requires complicated adjustment. In order to eliminatethis problem, in the present invention, the coil TC constitutes aresonance circuit that includes the movable portion Rot. This specificaspect of the present invention is explained in reference to FIG. 9.

FIG. 9 shows the characteristics that are achieved when the movableportion Rot is constituted of a good conductor such as copper, aluminumor the like and a resonance circuit that resonates with the operatingfrequency fr is constituted with the coil TC, the resonance capacitorCr, the movable portion Rot in a state in which the coil TC issufficiently close to the movable portion Rot, i.e., L=L1. When themovable portion Rot is far enough away from the coil TC (L=∞), the Qfactor between the movable portion Rot and the coil TC increases andalso the self inductance of the coil TC increases. Consequently, theresonance frequency shifts to a frequency f1, which is lower than theoperating frequency fr.

When the coil TC further approaches the movable portion Rot so that thedistance L2<L1, the Q factor of the coil TC is reduced and theinductance also becomes reduced. Consequently, the resonance frequencyshifts to a frequency f2, which is higher than the operating frequencyfr. Thus, if the coil TC moves away from the movable portion Rot to aspecific operating frequency fr, the output level e of the rotationsensor is set to e0 (<e1),whereas, if the coil TC comes too close, thisoutput level e is set to e2<e1 and, in either case, the output level eis reduced. Therefore, the error described above can be prevented bysetting the threshold value et of the level detection circuit 3 betweenthe output level e1 when the distance L is at L1 and the higher level ofthe following two levels, i.e., level e0 when the coil TC has fallendown or the level e2 when the coil TC has come too close.

FIG. 10 shows yet another embodiment of the apparatus for confirmingstop of movable portion according to the present invention. The devicein FIG. 10 includes a rectifying circuit RC3, a rectifying circuit RC4,an on-delay circuit OND1, a rectifying circuit RC5, a capacitor C7 forAC coupling, a clamping diode D5, an on-delay circuit OND2, a rectifyingcircuit RC6 and an off-delay circuit OFD.

The rectifying circuit RC3 rectifies an AC output signal k40 of thelevel detection circuit LV1 (see FIG. 2) to a positive voltage signal.The rectifying circuit RC4 rectifies the AC output signal k40 of thelevel detection circuit LV1 to a negative voltage signal. The on-delaycircuit OND1 operates with a specific delay time relative to the rise ofthe output signal of an output signal k41 of the rectifying circuit RC3.The rectifying circuit RC5 rectifies an AC output signal from theon-delay circuit OND1 to generate an output signal k51. The capacitor C7for AC coupling transmits the AC component of an output signal k42 ofthe rectifying circuit RC4. The AC signal k43 that is transmitted isclamped to the source potential Vcc at the clamping diode D5 to be inputto the on-delay circuit OND2. The on-delay circuit OND2 uses the signalk43, which is transmitted via the capacitor C7, as an input signal. Therectifying circuit RC6 rectifies an AC output signal from the on-delaycircuit OND2 to generate an output signal k52. The OR (wired OR) of theoutput signal k51 of the rectifying circuit RC5 and the output signalk52 of the rectifying circuit RC6 is input to the off-delay circuit OFD.

The route through which the AC output signal k40 of the level detectioncircuit LV1 is converted to the DC output signal k41 of the rectifyingcircuit RC3 and then is transmitted as the output signal k51 of therectifying circuit RC5 through the on-delay circuit OND1 and the routethrough which the AC output signal k40 of the level detection circuitLV1 is converted to an output signal k42 of the rectifying circuit RC4and is then transmitted as the DC output signal k52 of the rectifyingcircuit RC6 via the on-delay circuit OND2 are constituted, as far as thecircuit structure is concerned, to have a function identical to that ofthe route through which the signals are transmitted from the leveldetection circuit LV1 through the on-delay circuit OND in FIGS. 2 and 7except for the circuit structures of the rectifying circuits RC3 and RC4and the signal transmission path constituted with the capacitor C7 andthe diode D5.

Next, in reference to the time chart shown in FIG. 11, the operation ofthe circuit shown in FIG. 10 is explained. The output signal k40 of thelevel detection circuit LV1 is rectified at the rectifying circuit RC3and is generated as a positive rectified output signal k41. Thisrectified output signal k41 changes between the source potential Vcc(logical value 0) and a positive output voltage (logical value 1) whichis at a higher level than the source potential Vcc, in conformance tothe indentations Py1 and Py2 of the movable portion Rot, as shown inTime Chart (a) in FIG. 11. The shaded areas indicate the time blocksover which the rectified DC output signal k40 is generated.

The output signal k51 of the on-delay circuit OND1 is generated with adelay corresponding to the rise delay time Ton1 of the on-delay circuitOND1 after the rectified output signal k41 is generated, as shown inTime Chart (d). Then, as shown in FIG. 5, the duration of outputdissipation time constituted of the time Tof1 constitutes wait time.

The output signal k42 of the rectifying circuit RC4, which rectifies theoutput signal k40 of the level detection circuit LV1 to a negativesignal, changes between the source potential Vcc (logical value 1) andthe negative output voltage (logical value 0) which is at a lower levelthan the source potential Vcc, in conformance to the indentations Py1and Py2 of the movable portion Rot, as shown in Time Chart (b). Theshaded areas indicate the time blocks over which the rectified outputsignal k42 is generated. This output signal k42 is input to the on-delaycircuit OND2 as a signal k43 (see Time Chart (c) in FIG. 11) via thecapacitor C7 and the clamping diode D5. Since the signal k43 is clampedat the source potential Vcc by the diode D5, the level of the logicalvalue 0 is set to the source potential Vcc, as shown in Time Chart (c).The output signal k52 (see Time Chart (e)) is obtained through theon-delay circuit OND2 and the rectifying circuit RC6 is generated with adelay equivalent to the rise delay time Ton2 of the on-delay circuitOND2 after the signal k43 is generated, and then, after the signal k43has dissipated, a wait state exists until the output off timeconstituted of the time Tof2 elapses.

The off-delay circuit OFD uses the OR signal k50 constituted of theoutput signal k51 of the rectifying circuit RC5 and the output signalk52 of the rectifier circuit RC6 as its input signal. In the OR signalk50, time blocks where the logical value is set to 0 (low level blocks)are generated by the rise delay times of the two on-delay circuits OND1and OND2, as shown in Time Chart (f) and, as a result, the length oftime over which it is continuously off is reduced compared to the outputoff time in the on-delay circuit shown in FIG. 5.

This period of time over which the output is continuously off issignificant from the viewpoint of safety. In other words, when themovable portion Rot starts to rotate at high speed after stoppingtemporarily, the output signal from the on-delay circuit dissipatesimmediately because of the resulting rotation signal. However, theoutput signal from the off-delay circuit does not dissipate immediatelyand there will be a delay corresponding to the fall delay time of theoff-delay circuit. Thus, as far as safety is concerned, it is desirablethat the delay time of the off-delay circuit be short. In the embodimentshown in FIG. 10, a function for low speed judgement effected by theanti-phase signal of the output signal from the level detection circuitLV1 is added to the on-delay circuit OND1 shown in FIGS. 2 and 7, andthe function of the off-delay circuit OFD is to be incorporated in theOR output signal k50 constituted of the output signals k51 and k52 fromthe on-delay circuits OND1 and OND2. This makes it possible to reducethe delay time caused by the off-delay circuit OFD.

In FIG. 12, an optically coupled circuit PC is employed in place of thenegative rectifying circuit RC4 shown in FIG. 10. The optically coupledcircuit PC includes an optically coupled element PC1 constituted with alight emitting element PT1 and a light receiving element PD1, a currentlimiting resistance R6 and a load resistance R7 for the light emittingelement PD1. Note that the same reference numbers as those in FIG. 10are assigned to indicate identical components.

An output current signal k40 from the level detection circuit LV1 isprovided for the light emitting element PT1 via the resistance R6. Theoptical output signal from the light emitting element PT1 is received atthe light receiving element PD1 and when this happens, the terminalvoltage of the load resistance R7 changes to generate a signal k42. Thesignal k42 is output with its phase inverted relative to the opticalsignal from the light emitting element PT1. In addition, since the highfrequency component is not transmitted in an optically coupled element,the signal K42 forms a waveform identical to that shown in Time Chart(b).

Note that while FIGS. 1 and 6 show the indentations and projections ofthe movable portion as deformations of contour, it is obvious that themagnetic deformation does not necessarily have to be based on shape. Inother words, it is obvious that similar advantages can be obtained byusing insulating material and conducting material instead ofindentations and projections.

While the present invention has been explained in detail in reference tothe preferred embodiments, it will be obvious to a person skilled in theart to which the present invention pertains, that it is not limited tothese embodiments and that a number of variations are possible basedupon the teachings and the spirit of the present invention.

INDUSTRIAL APPLICABILITY

The present invention offers the following possibilities for industrialapplication:

(a) An apparatus for confirming stop of movable portion in which thedelay in notification of stop of the movable portion is reduced, can beprovided.

(b) An apparatus for confirming stop of movable portion that issuesnotification of movable portion stop after detecting that the coil iscombined with the movable portion correctly with no risk of it coming incontact with the movable portion, can be provided.

(c) An apparatus for confirming stop of movable portion in which thenotification of movable portion stop is issued based upon verificationthat the movable portion has been monitored until immediately before thenotification is issued, can be provided.

(d) An apparatus for confirming stop of movable portion that is capableof generating a signal to indicate movable portion stop based uponverification made with a startup switch at the time of startup, can beprovided.

(e) An apparatus for confirming stop of movable portion that issuesnotification of movable portion stop based upon verification that themovable portion has been monitored even at the time of startup, can beprovided.

(f) An apparatus for confirming stop of movable portion in which thedelay time of dissipation of the movable portion stop signal can bereduced when the movable portion has started rotating or moving, can beprovided.

(g) An apparatus for confirming stop of movable portion that facilitatesadjustment can be provided.

We claim:
 1. An apparatus for confirming stop of movable portion fordetecting stop of a metal movable portion comprising:detection meansincluding a coil provided in close proximity to a surface of saidmovable portion and detecting changes in impedance generated at saidcoil caused in response to indentations and projections provided at saidsurface of said movable portion to output a detection signal; a speedjudgement circuit, to which said detection signal output from saiddetection means is provided, continuously generating a high level outputsignal when intervals between changes in said detection signal becomelonger than a specific period; a level detection circuit, to which saiddetection signal output from said detection means is provided,generating a high level output signal when said detection signal is ator higher than a specific level; and an AND circuit, to which saidoutput signal from said speed judgement circuit and said output signalfrom said level detection circuit are provided, generating an outputsignal resulting from AND calculation of said output signals.
 2. Anapparatus for confirming stop of movable portion according to claim 1,wherein:said speed judgement circuit includes an on-delay circuit and anoff-delay circuit; said on delay circuit, to which a signal thatcontains a component of said detection signal output from said detectionmeans is provided, generates an output signal that responds immediatelyto a fall of said signal and rises with a delay of a specific length oftime after a rise of said signal; and said off-delay circuit respondsimmediately to a rise of said output signal output from said on-delaycircuit, causes said output signal to be delayed by a specific length oftime when said output signal falls and provides an output signal to saidAND circuit.
 3. An apparatus for confirming stop of movable portionaccording to claim 2, further comprising:means for generating a highfrequency signal, wherein:said high frequency signal thus generated issuperimposed on said detection signal output from said detection meansand said signal thus superimposed is provided to said speed judgementcircuit.
 4. An apparatus for confirming stop of movable portionaccording to claim 3, wherein:said speed judgement circuit includes alow-pass filter which, provided at a stage preceding said on-delaycircuit, generates a DC signal at high level when said superimposedsignal contains a high frequency component and outputs a signal thatresponds to a low frequency component based upon said detection signal.5. An apparatus for confirming stop of movable portion according toclaim 4, wherein:said low-pass filter is constituted with a voltagedoubling rectifying circuit, which includes a large capacity couplingcapacitor and a small capacity smoothing capacitor.
 6. An apparatus forconfirming stop of movable portion according to claim 1, furthercomprising:a self holding circuit, wherein:said self holding circuituses change in an output signal from said detection means as a triggerinput signal and uses an output signal from said speed judgement circuitas a reset input signal; and said AND circuit, to which output signalsare provided from said self holding circuit and said level detectioncircuit, generates an output signal resulting from AND calculation ofsaid output signals.
 7. An apparatus for confirming stop of movableportion according to claim 6, further comprising:a means for startupswitching that is operated from outside, wherein:said means for startupswitching is provided with a contact point for providing said selfholding circuit with a trigger input signal.
 8. An apparatus forconfirming stop of movable portion according to claim 7, wherein:saidmeans for startup switching is provided with another contact point thatis closed when said trigger input signal is turned off; and another ANDcircuit is provided, which uses signal provided through said anothercontact point of said means for startup switching when said triggerinput signal for said self holding circuit is turned off and an outputsignal from said self holding circuit as input signals to generate anoutput constituted with an AND thereof.
 9. An apparatus for confirmingstop of movable portion according to claim 6, wherein:said speedjudgement circuit includes an on-delay circuit and an off-delay circuit;said on delay circuit, to which a signal that contains a component ofsaid detection signal output from said detection means is provided,generates an output signal that responds immediately to a fall of saidsignal and rises with a delay of a specific length of time after a riseof said signal; and said off-delay circuit responds immediately to arise of said output signal output from said on-delay circuit, causessaid output signal to be delayed by a specific length of time when saidoutput signal falls and provides an output signal to said AND circuit.10. An apparatus for confirming stop of movable portion according toclaim 9, further comprising:means for generating a high frequencysignal, wherein:said high frequency signal thus generated issuperimposed on said detection signal output from said detection meansand said signal thus superimposed is provided to said speed judgementcircuit.
 11. An apparatus for confirming stop of movable portionaccording to claim 10 wherein:said speed judgement circuit includes alow-pass filter which, provided at a stage preceding said on-delaycircuit, generates a DC signal at high level when said superimposedsignal contains a high frequency component and outputs a signal thatresponds to a low frequency component based upon said detection signal.12. An apparatus for confirming stop of movable portion according toclaim 11, wherein:said low-pass filter is constituted with a voltagedoubling rectifying circuit, which includes a large capacity couplingcapacitor and a small capacity smoothing capacitor.
 13. An apparatus forconfirming stop of movable portion according to claim 1, wherein:saidspeed judgement circuit includes two on-delay circuits and an off-delaycircuit, said two on-delay circuits to which a signal containing saiddetection signal output from said detection means is commonly providedgenerate output signals whose phases are inverse from each other; andsaid off-delay circuit is provided with an OR signal constituted of saidoutput signals from said two on-delay circuits.
 14. An apparatus forconfirming stop of movable portion according to claim 13 furthercomprising:means for generating a high frequency signal, wherein: saidhigh frequency signal thus generated is superimposed on said detectionsignal output from said detection means and said signal thussuperimposed is provided to said speed judgement circuit.
 15. Anapparatus for confirming stop of movable portion according to claim 14wherein:said speed judgement circuit includes a low-pass filter which,provided at a stage preceding said on-delay circuit, generates a DCsignal at high level when said superimposed signal contains a highfrequency component and outputs a signal that responds to a lowfrequency component based upon said detection signal.
 16. An apparatusfor confirming stop of movable portion according to claim 15,wherein:said low-pass filter is constituted with a voltage doublingrectifying circuit, which includes a large capacity coupling capacitorand a small capacity smoothing capacitor.
 17. An apparatus forconfirming stop of movable portion according to claim 1, wherein:saidcoil constitutes a resonance circuit that includes said movable portion.